1. Field of the Invention
The present invention relates to atomic-size conductive fine wires necessary for wiring interconnections between elements or between elements and electrodes in an integrated circuit of these elements of atomic-size or nanometer-size, and to atomic-size switches made of atomic-size fine wires having an electronic switching function.
2. Description of the Related Art
High integration and high speed operation of logic circuits using MOS transistors are progressing more and more nowadays as well known. Such high integration and high speed operation are realized by fine patterns of each constituent element, and a minimum patterning size of transistors is now in the order of as small as 0.1 micron. Vigorous efforts are still made in order to realize more fine structures without changing fundamental principles of such conventional technology. However, with the same conventional technology, it is supposed that more fine structures will encounter some limits sooner or later, because of various factors such as expansion of a depletion layer of a p-n junction, statistical errors, and increase of power consumption.
Under such circumstances, studies of microdevices have been made, basing upon principles different from conventional principles. For example, various elements capable of reducing their size to atomic-size or nanometer-size have been proposed, such as atomic switches (refer to JP-A-5-175513). Although each specific element is given some approach to microminiaturization as above, it is important for microminiaturization of an integrated circuit not only to make each integrated element fine but also to make fine a wiring interconnection between elements for signal transfer. With advanced fine-pattern fabrication techniques, it is already possible to fabricate a conductive fine wire having a cross section of 1 nm square. For example, such conductive fine wires can be manufactured by using techniques such as techniques for embedded atomic fine wires (refer to JP-A-7-30093). It is still desired, however, to establish techniques of further reducing the size of fine wires without degrading conductivity thereof, in order to positively utilize the specific features of atomic-size elements.
A fine wire structure having a width of atomic-size can be manufactured by using techniques of finely patterning a solid surface by a scanning tunneling microscope, as reported for example in Science, 268 (1955), pp. 1590-1592. These techniques only are not sufficient, however, to fabricate atomic-size fine wires having structural stability and conductivity. For example, an atomic-size fine wire formed by extraction of a row of hydrogen atoms from the surface of hydrogen-terminated silicon shows conductivity as reported in Physical Review B, 52 (1995), pp. 10768-10771. However, this fine wire is likely to become non-conductive through adsorption of environmental atoms or molecules so that it is used only under an ultrahigh vacuum atmosphere. Anyone of atomic-size conductive fine wires reported to date becomes non-conductive in very short time because of the above-described reason or because of migration of constituent atoms likely to be caused by thermal vibrations even at about a room temperature. In this context, conventional conductive fine wires are not structurally stable. On the other hand, most of structurally stable atomic-size fine wires are non-conductive. Conductive fine wires were successfully formed occasionally in the past. However, the reason of conductivity and manufacture conditions could not be made clear at all. As described above, it can be said that fabrication methods of atomic-size fine wires with structural stability and conductivity are still not known.